Devices for inputting a coordinate position manually to a host computer include electromagnetic induction devices, electrostatic capacitance devices, transparent electrode devices, and optical detection devices. Of these the optical devices are receiving attention since they can be attached to the front of a display device, and simply by pressing an arbitrary point of the display device with a finger or the like, without connection to the detecting device, a particular coordinate position can be detected, and this provides reliability and operability.
A conventional example of this optical detection type of coordinate input device is shown in FIGS. 12 to 14. FIG. 12 is a perspective diagram showing the coordinate input device attached to the front of a display device, FIG. 13 shows a partial sectional view of the optical detecting element end, and FIG. 14 is a rear view of the internal construction of the coordinate input device with the rear cover removed. The coordinate input device is of roughly rectangular shape, and is principally constructed of a frame 1 with a central opening 2, a set of light emitting elements 4 such as LEDs and light detecting elements 5 such as phototransistors opposing each other on the edges of the reverse of the frame 1 or as shown in FIG. 12 on the side of the display screen 3a of the display device 3 which uses for example a CRT (cathode ray tube), and a calculation unit 6 which detects the position where the optical path between these sets of light emitting elements 4 and light detecting elements 5, and inputs to the host computer the coordinate position thereof.
Furthermore, in the opening 2 is provided an operating panel 2a formed of a VDT (video display terminal) filter, and by disposing this in front of the display screen 3a of the display device 3, and thereby dirt and dust are prevented from adhering to the screen 3a and the user's eyes are protected from strain. The light emitting elements 4 and the light detecting elements 5 have light emitting portions 4a and light detecting elements 5a fixed so as to be mutually facing to a base 7 attached to the frame 1. These light emitting elements 4 and light detecting elements 5 correspond to an area of the screen 3a for input use, and in order to detect only a particular operating area A, they are omitted from edge areas on each side so that the light paths do not intersect in the edge areas B. Furthermore on the front side of the light detecting portions 5a of the light detecting elements 5 is provided an optical baffle 8 in which are formed light transmitting apertures 8a of such a cross section and depth that the light from the corresponding light emitting element 4 can be received. Furthermore around the entire periphery of the apertures of the front of the optical baffle 8 and the front of the light emitting elements 4 is attached an infra-red filter 9 as a visible cutoff filter. Therefore on the side of the screen 3a of the operating panel 2a is established an optical path 12 not visible to the eye through the infra-red filter 9.
When a coordinate position is to be detected, as shown for example in FIG. 12 and FIG. 14, a finger 10 or the like is pressed from above the operating panel 2a at the position of the screen 3a to be input, whereupon since a light path 12 is established along the surface of the operating panel 2a, by scanning to energize the light emitting elements 4 in turn, in both the x direction and the y direction the obstructed light path 12 can be detected serially by the light detecting elements 5. Thus the obstructed light path 12 can be determined by the calculation unit 6, and the coordinate position can be output to a host computer not shown in the drawing.